The present invention relates to a multistage pump provided with modular internal components made of highly wearproof materials such as to give the pump a high specific fluid-dynamics performance.
As it is known, multistage electric pumps are essentially power-using machines constituted by an electric motor and a multistage pump which are mutually integrated; they are used to raise fluids, particularly water.
Conventional multistage pumps comprise a containment jacket shaped like a cylindrical tube. An impeller supporting shaft is arranged coaxially to the tube, and is connected to the driving shaft in a downward region and kept in position by a bush or the like in an upward region.
A plurality of impellers with radial vanes is rigidly anchored on said rotating shaft, coaxially to the containment jacket, in equidistant positions; each impeller is arranged opposite to an annular body which acts as a redirection-diffusion element for the fluid drawn by the respective impeller; each diffuser is rigidly coupled to the internal surface of said cylindrical jacket by means of an annular body which is substantially bowl-shaped and is generally termed "bowl".
Each assembly constituted by an impeller and the associated fixed diffuser thus constitutes a stage of the pump. Furthermore, each impeller with radial vanes is provided, in a front region, with a disk-like ring which closely faces the associated bowl-shaped element to avoid as much as possible unwanted transfers of fluid during pump operation.
The stream of fluid drawn by the impellers from a duct located at an end of the containment jacket is expelled from the other end of said jacket, where there possibly is a check valve suitable to prevent backflow. These known types of multistage pumps generally have impellers and diffusers made of metal or plastic materials which, after prolonged use, are subject to wear and thus to a progressive decrease in their fluid-dynamics performance and consequently in their volumetric efficiency. Furthermore, due to the rigidity of the structure of the stages, all the axial thrusts generated by the various stages are discharged onto a thrust bearing which is usually associated with the driving shaft; in addition, the structure of these known pumps does not prevent any abrasive particles contained in the drawn fluid from penetrating between the front ring of the impellers and the surface of the bowls which face said ring and thus damaging the ring and the associated impellers.
In practice, therefore, the nominal rotation rate and consequently the specific fluid-dynamics performance and volumetric efficiency of conventional pumps are affected by the respective structural characteristics, by the materials used and by the dimensions, particularly by the diameter of the containment jacket.